1. Field of the Invention
The present invention relates to a substrate supporting apparatus used in an apparatus for processing, for example, a semiconductor wafer or the like and a manufacturing method therefor.
2. Description of the Related Art
In semiconductor manufacturing processes, a substrate supporting apparatus that has a heating function and the like is used to process a substrate, such as a wafer. The substrate supporting apparatus has a plate member for supporting the substrate. The substrate is placed on the upper surface of the plate member.
If any particulate dust, a contributor to contamination, exists on the plate member and adheres to the reverse side of the wafer, it lowers the quality of semiconductors. To prevent adhesion of the particulate dust, therefore, an attempt is made to arrange a plurality of small spacer members on the upper surface of the plate member and place the wafer on the spacer members. Described in FIGS. 2a and 2b of Japanese Patent Publication No. 2001-508599, for example, are a plate member and a plurality of small spacer members that are arranged on the upper surface of the plate member.
Each of the spacer members is in the form of a sphere or column, which is fitted into a pit in the plate member by press fit or some other technique. The spacer members are formed of a ceramic or another material that has brittleness and a thermal expansion coefficient lower than that of metal. Possibly, on the other hand, the plate member may be formed of an aluminum alloy or other material that has a high thermal expansion coefficient.
In some cases, the plate member and the spacer members may be considerably different in thermal expansion coefficient. If the substrate supporting apparatus is exposed to high temperature in, for example, a wafer treatment process, in such cases, the spacer members, which are lower in thermal expansion coefficient than the plate member, may possibly slip out of their corresponding pits of the plate member. The spacer members can be made less easy to slip out of the pits by only being brought tightly into contact with the respective inner surfaces of the pits. If this is done, however, the plate member thermally contracts to a higher degree than the spacer members do when the substrate supporting apparatus is cooled, for example. Accordingly, an excessive stress is generated in the spacer members and may possibly break the spacer members that are brittle. Thus, the conventional substrate supporting apparatus has a problem in structural solidity to resist a heat cycle or the like.
In the conventional substrate supporting apparatus, moreover, the upper end of each spacer member simply projects from the upper surface of the plate member. If any particulate dust that causes contamination exists on the upper surface of the plate member, in this arrangement, it moves from the upper surface of the plate member toward the spacer member and may possibly adhere to the reverse side of the wafer.